Initiation, progression, and completion of the mammalian cell cycle are regulated by various cyclin-dependent kinase (CDK) complexes, which are critical for cell growth. These complexes comprise at least a catalytic (the CDK itself) and a regulatory (cyclin) subunit. Some of the more important complexes for cell cycle regulation include cyclin A (CDK1—also known as cdc2, and CDK2), cyclin B1-B3 (CDK1), cyclin D1-D3 (CDK2, CDK4, CDK5, CDK6), cyclin E (CDK2). Each of these complexes is involved in a particular phase of the cell cycle. Not all members of the CDK family are involved exclusively in cell cycle control, however. Thus CDKs 7, 8, and 9 are implicated in the regulation of transcription, and CDK5 plays a role in neuronal and secretory cell function.
The activity of CDKs is regulated post-translationally, by transitory associations with other proteins, and by alterations of their intracellular localisation. Tumour development is closely associated with genetic alteration and deregulation of CDKs and their regulators, suggesting that inhibitors of CDKs may be useful anti-cancer therapeutics. Indeed, early results suggest that transformed and normal cells differ in their requirement for e.g. cyclin A/CDK2 and that it may be possible to develop novel antineoplastic agents devoid of the general host toxicity observed with conventional cytotoxic and cytostatic drugs. While inhibition of cell cycle-related CDKs is clearly relevant in e.g. oncology applications, this may not be the case for the inhibition of RNA polymerase-regulating CDKs. On the other hand, inhibition of CDK9/cyclin T function was recently linked to prevention of HIV replication and the discovery of new CDK biology thus continues to open up new therapeutic indications for CDK inhibitors (Sausville, E. A. Trends Molec. Med. 2002, 8, S32-S37).
The function of CDKs is to phosphorylate and thus activate or deactivate certain proteins, including e.g. retinoblastoma proteins, lamins, histone H1, and components of the mitotic spindle. The catalytic step mediated by CDKs involves a phospho-transfer reaction from ATP to the macromolecular enzyme substrate. Several groups of compounds (reviewed in e.g. Fischer, P. M. Curr. Opin. Drug Discovery Dev. 2001, 4, 623-634) have been found to possess anti-proliferative properties by virtue of CDK-specific ATP antagonism.
WO 98/05335 (CV Therapeutics Inc) discloses 2,6,9-trisubstituted purine derivatives that are selective inhibitors of cell cycle kinases. Such compounds are useful in the treatment of autoimmune disorders, e.g. rheumatoid arthritis, lupus, type I diabetes, multiple sclerosis; treating cancer, cardiovascular disease, such as restenosis, host v graft disease, gout, polycystic kidney disease and other proliferative diseases whose pathogenesis involves abnormal cell proliferation.
WO 99/07705 (The Regents of the University of California) discloses purine analogues that inhibit inter alia protein kinases, G-proteins and polymerases. More specifically, the invention relates to methods of using such purine analogues to treat cellular proliferative disorders and neurodegenerative diseases.
WO 97/20842 (CNRS) also discloses purine derivatives displaying antiproliferative properties which are useful in treating cancer, psoriasis, and neurodegenerative disorders.
The present invention seeks to provide new 2,6,9-substituted purine derivatives, particularly those having antiproliferative properties.